Transmission/streaming of video over error prone networks is associated with packet erasures when channel conditions are not favourable. To avoid a large drop in video quality at the receiver due to intra- and inter-frame propagation of such errors, error resilience at the encoder and use of error concealment at the decoder are necessary. Error concealment methods described in [Y. Wang, S. Wenger, J. Wen, and A. K. Katsaggelos, “Error Resilient Video Coding Techniques-Real time video communications over unreliable networks,” IEEE Signal Processing Magazine, vol. 17, pp. 61-82, 2000] and [Y. Wang and Q.-F. Zhu, “Error Control and Concealment for Video Communication: A Review,” Proceedings of the IEEE, vol. 86, pp. 974-997, 1998] estimate lost information by employing the correlation that exists between a missing macroblock (MB) and the temporally and spatially adjacent ones. They can be classified in two categories. Temporal concealment methods estimate lost motion vectors and then use these for motion compensated temporal replacement of the lost MBs. Spatial concealment methods rely on spatially adjacent macroblocks for estimating missing pixels usually through an interpolation process.
Although not normative, the H.264 joint model (1M) decoder implements both spatial and temporal error concealment for missing intra and inter coded macroblocks—see [Y.-K. Wang, M. M. Hannuksela, V. Varsa, A. Hourunranta, and M. Gabbouj, “The error concealment feature in the H.26L test model,”, ICIP, USA, 2002]. Temporal concealment (employed solely for lost MBs in P or B frames), is implemented based on the boundary matching algorithm (BMA) described in [W.-M. Lam and A. R. Reibman, “Recovery of lost or erroneously received motion vectors,” ICASSP, USA, 1993] which predicts the motion vector (MV) of one missing macroblock out of a list of candidate MVs coming from 4-neighboring MBs (or 8×8 blocks of these) and including the zero MY. The MY that results in the smallest boundary matching error (BME) is then used for motion compensated replacement of the missing pixels from a previously decoded frame. Spatial concealment is employed for intra coded frames.